Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $206.62   8.494%   $224.1703   $224.17   $224.15   $224.20  
  Purchase #2 $101.85   13.525%   $115.6252   $115.63   $115.65   $115.60  
  Purchase #3 $131.80   11.578%   $147.0598   $147.06   $147.05   $147.10  
  Purchase #4 $69.91   10.265%   $77.0863   $77.09   $77.10   $77.10  
  Purchase #5 $21.98   6.760%   $23.4658   $23.47   $23.45   $23.50  
  Purchase #6 $153.89   10.755%   $170.4409   $170.44   $170.45   $170.40  
  Purchase #7 $40.70   10.305%   $44.8941   $44.89   $44.90   $44.90  
  7 purchase totals = $726.75       $802.7424   $802.75   $802.75   $802.80